In order to prevent the possibility of an infinite recursion, (basically software cancer proliferating in your computer’s memory,) it is not possible to use future lengths for past measurements (X=X+2.) There does appear to be a way to edit your History, (at great risk to destroying your pattern,) which @Grace seems to be familiar with, (I have yet to figure it out,) which she posted about here:
Your best bet may be to make the armscye of the bodice after making the sleeve.
